122 NORTH AMERICAN INDEX FOSSILS. 



163. C. cretaceum Whitfield. (Fig. 1362.) Devonic. 

 Moderately and somewhat irregularly expanding, slightly curv- 

 ing and of oval section; ventral surface more arcuate than dorsal; 

 siphuncle small, near the venter, slightly nummuloidal ; septa close, 

 deeply concave; living chamber comparatively short; lip with 

 broad, shallow sinuosity on each side. 



Onondaga (Columbus) limestone of Ohio. 



164. C. metula Hall. (Fig. 1363.) Devonic. 

 Differs from the preceding in the regular curvature, regular 



expansion, more slender form; sutures slightly lobed on dorsal 

 and with faint forward sweep on ventral side ; aperture very gently 

 contracted. 



Onondaga of New York and Ontario. 



LXIV. Oncoceras Hall. 



Differs from the preceding in being laterally compressed, with 

 the living chamber more flattened laterally, and the aperture elon- 

 gated and often subtrigonal, but typically open. Ordovicic-Siluric. 



Fig. 1363. Cydostomiceras metula. (After FiG. 1364. Oncoceras pristinum, 

 Hall, Pal. N. Y., V.) sectional view. (After Ruedemann, 



Bull. 90, N. Y. State Mus. ) 



165. 0. pristinum Ruedemann. (Fig. 1364.) Ordovicic. 



Small, breviconic cyrtoceracones, exogastric, and slightly curved ; 



dorsoventral and lateral diameters as 9:7; dorsum more rounded ; 



